Shoulder replacement surgery (referred to medically as “shoulder arthroplasty,” or “total shoulder arthroplasty”) involves removal of a portion of the glenoid surface (the socket portion of the ball-and-socket shoulder joint), performed by a reamer (or “reaming device”). Reamers generally consist of one or more spinning blades that remove bone from the glenoid surface. Such reamers generally are cannulated, such that they are inserted over a guide wire and/or guide pin, to the location of the reaming. After the glenoid surface is so prepared, a glenoid component of a prosthetic shoulder joint is placed. A portion of the patient's humerus also may be replaced in such procedures. The depth of the wound created while reaming the glenoid surface and the tension of surrounding soft tissues make it difficult to see landmarks accurately, often making glenoid preparation the most challenging step. Additionally, the humeral head (the ball portion of the shoulder joint, that fits into the glenoid) often interferes with the reamer's access to the glenoid, and the reamer can damage the humeral head and surrounding soft tissues as the reamer is inserted past the humeral head and then subsequently removed after reaming the glenoid.
Total shoulder arthroplasty has undergone significant refinement in the last decade. Advances in implants and instruments designed to aid the insertion of implants have greatly improved the accuracy and efficiency of the operation. Even so, prior attempts at minimizing damage to the humeral head and surrounding tissues each come with significant disadvantages. For example, such techniques have involved forgoing the use of the guide pin (which reduces accuracy of the procedure), bending the guide pin while advancing the reamer past the humeral head (which may deform and/or break the guide pin, resulting in inaccurate reaming and/or a broken guide pin), and/or modifying the reamer, such as by cutting out a portion of the circular reamer head, for example to create a “bowtie” or “propeller” shape, to make advancement past the humeral head easier. Despite these improvements, insertion of the glenoid reamer is still often difficult and potentially traumatic to the soft tissues or bony structures such as the deltoid muscle, strap muscles, and the lesser tuberosity.